This invention relates to drive systems and more particularly to a reversible web supply and take up mechanism.
In the past there have been provided various web drive systems which have a working material or web drawn from a supply reel, used, and wound on a take up reel. Such systems are typically found in typewriters or printers wherein the web material is an inked cloth or similar type ribbon. The ribbon life is not fully used the first time it is printed with, and can be printed with several times before the ink is depleted and its useful life is over.
The web is drawn from the supply reel until the end of the web is reached. Normally the web has its ends firmly attached to the supply reel and take up reel so that it cannot be inadvertently removed from either reel. When the end of the web is reached, the take up reel will have the entire web wound thereon. The direction of the web travel is reversed and the take up reel now becomes the supply reel and the supply reel becomes the take up reel. This reversal process continues several times until the useful life of the web is reached.
Various mechanisms have been supplied in the past to sense when the end of the web is reached so that the supply and take up reels can reverse direction. One method was to place a metal stop near the end of the web at each end. The metal stop was sensed by mechanical lever means which reverse a gear drive so that the direction of rotation of the reels was reversed. Such a system has been used on mechanical typewriters for years and is a simple, inexpensive system. However, it required the addition of the mechanical stops affixed to the ribbon and is practical with ribbons having a narrow width, such as a typewriter ribbon. Furthermore, as the system is entirely mechanical, it tends to wear out with use and required constant maintenance and adjustments. Furthermore, a snag, twist or catching of the ribbon can inadvertently cause the ribbon to reverse direction before its end is reached.
Another type of system employs dual motors, one each to drive the supply and take up reels. When one of the reels is acting as the take up reel, that motor is energized and pulls the web from the supply reel. The supply reel motor could either be disengaged from the supply reel, or can be designed so that it will not produce a prohibitive amount of drag on the supply reel resulting in the web not being easily withdrawn therefrom. When the end of the web is reached the motor which was attached to the supply reel, is now energized and becomes the take up reel motor. The previous take up reel motor is de-energized and performs as the supply reel motor previously did. A problem with this system is that the two motor drive systems employ mechanical sensing devices which do not repeat reliably. This causes drive failures and poor ribbon utilization. Also, the system is expensive in that two drive motors must be used.
Applicant's invention solves the problems of the prior art in that it utilizes a single reversible motor which minimizes cost. Attached to the output of the motor is a reversible mechanical device system which can provide power to either the take up or supply reels. The power is first supplied to one reel and then the other upon reversal of the direction of the output shaft of the motor. An electronic sensing device senses motor current and reverses direction of the motor when the end of the web is reached. Each end of the web is affixed to either the supply or take up reel so that it cannot be removed from the reel. Thus, when the end of the web is reached, the motor current rises dramatically as this is the stalled or locked rotor condition of the motor. The rise in current is sensed by the sensing device and a reversing motor controller reverses the direction of the output shaft of the motor. The gear mechanism drive is reversed from supplying power to the reel which was previously the take up reel to the reel which was previously the supply reel. The web direction then reverses and the web is moved from the reel which was previously the take up reel to the reel which was previously the supply reel. The web reversal continues until the life of the ribbon is exhausted.